TL;DR: A stop loss order is an instruction to sell if a stock falls to a trigger price you set in advance. Illustrative example only: you buy at $50 and set a stop at $45. If the price falls to $45, the order triggers and becomes a market order to sell, so your planned maximum loss is $5 per share before slippage and gaps, since $50 minus $45 equals $5. Planned is the key word. If the stock gaps down overnight from $48 to $40, the order triggers at the open and fills near the available price, not at $45, and the loss is larger than planned. A stop loss enforces discipline. It does not guarantee a price.
Key Takeaways
- A standard stop loss becomes a market order once triggered. Execution is prioritised after the trigger, with no price floor.
- Your planned loss per share is the entry price minus the stop price. Your actual loss can be larger when prices gap or move fast.
- A stop limit order adds a price floor after the trigger, regaining price control but risking no fill at all in a fast fall.
- Stops set too close to the current price are triggered by ordinary price movement, selling you out of positions you wanted to hold.
- A stop loss is a tool for enforcing a decision made in advance. It is not a substitute for position sizing, covered in position sizing explained.
How does a stop loss order work, step by step?
You buy a stock and, at the same time or later, you tell your broker a trigger price below the current price. Nothing happens while the price stays above the trigger. If the traded price reaches the trigger, the stop order activates and, in its standard form, becomes a market order, which fills at the next available price as described in what is a market order.
Work through the illustrative example in full. All figures in this section are illustrative. You buy at $50 per share. You set the stop at $45. The distance between entry and stop is $50 minus $45, which equals $5 per share. On a position of 100 shares, the planned maximum loss is $5 multiplied by 100, which equals $500 before fees, slippage, and gaps. If the stock declines gradually to $45 during trading hours in an orderly market, the triggered market order will usually fill close to $45, and the realised loss will be close to the planned $500. The mechanism works as intended in that orderly case, and it is important to understand that this is the case the tool was designed for.
Now the disorderly case, which every user of stops must understand before relying on one. The stock closes at $48. Overnight, the company reports bad news. The stock opens at $40. Your stop at $45 was passed entirely during the gap, so the order triggers at the open and fills near the available opening price, around $40 in this illustration, not at $45. The loss is about $10 per share, since $50 minus $40 equals $10, roughly double the planned $5. No broker error occurred. A stop order is a trigger, not a price promise, and gaps are the clearest proof of that distinction.
How is a stop loss different from a limit order and a stop limit order?
A limit order, covered in what is a limit order, is an order to trade at your price or better, active from the moment you place it. A stop order is dormant until triggered, then prioritises getting out. A stop limit order combines the two: once the trigger is reached, it becomes a limit order at a floor price you set. That floor protects you from a very poor fill, but in a fast fall no buyer may trade at your floor, so the order can remain unfilled while the price keeps falling and you still hold the position. Choosing between a stop market and a stop limit order is choosing which failure you prefer in a crash: a fill at a bad price, or possibly no fill at all.
Broker definitions and trigger methods vary. Some brokers trigger on the last traded price, others on a quote, and handling outside regular hours differs, which matters because gaps often occur between sessions, as our guide to premarket and after hours trading explains. Read your broker's exact terms for the order type before using it.
Where do stop losses help, and where do they hurt?
They help when the main risk is your own behaviour: holding a losing position long past the point where your original reasoning has failed, because admitting the error feels worse than keeping the loss. A stop set at purchase time converts a future emotional decision into a present mechanical one. They also help investors who cannot watch prices during the day, because the instruction sits with the broker rather than in a reminder note.
They hurt when they are set inside the stock's normal trading range. Every stock moves up and down by some amount in an ordinary week. A stop placed within that ordinary movement will be triggered by noise, realising a small loss and removing you from a position that may then recover without you. This whipsaw cost is the standing price of the tool. Long term investors in broad funds often decide that position sizing and diversification manage their risk better than stops do, while shorter horizon traders treat stops as essential. Neither view is a rule. The honest test is whether the stop distance you have chosen matches the price movement you genuinely consider a broken case, rather than a bad week.
This article is educational information about how an order type works, not financial advice and not a recommendation to buy, sell, or set a stop on any security. Whether a stop loss suits a given position depends on the investor's own circumstances and judgement.
Sources and method
- Target keyword: "what is a stop loss order" from .saeo/keywords.yaml (queue entry added 2026-10-29). No search volume or difficulty figure is claimed; both are recorded as unknown in the queue entry.
- All prices are labelled illustrative examples. Arithmetic verified for this draft on 2026-10-29: $50 minus $45 equals $5; $5 multiplied by 100 shares equals $500; $50 minus $40 equals $10.
- Internal links checked against existing drafts in this folder on 2026-10-29: position-sizing-explained, what-is-a-market-order (drafted in this same run), what-is-a-limit-order, premarket-and-after-hours-trading-explained.
